Archive for September, 2013

Moon jellyfish (Aurelia aurita) form huge blooms in many of our oceans (guardian.co_.uk).

Increasing jellyfish blooms are a symptom of the challenged health of our oceans. Where fish have been fished down or out, jellyfish thrive. Where oxygen levels drop too low for many organisms, jellyfish thrive. Where a community then flips from fish-dominated to jellyfish dominated, recovery is difficult to achieve.

Jellyfish blooms clog fishing nets, intake pipes of desalination and nuclear plants, cause mass mortality of salmon in coastal farms, decimate fisheries already in steep decline, and sting swimmers out of the water at beaches everywhere.

Nomura’s Jellyfish are giants, up to 200 kg and 2 meters in diameter, and do much damage to fishermen’s nets in the Sea of Japan (fastcompany.com).

In a new book Stung!: On Jellyfish Blooms and the Future of the Ocean, Lisha-ann Gershwin documents the ravages of jellyfish blooms and the deterioration of marine ecosystems, and her final conclusion is a very cold bath: we have permanently wrecked the oceans, we can’t fix what we have done, and all we can do now is adapt to the inevitable lousy changes that have already begun.

Box jellyfish (Cubomedusae) have powerful stings, and drive swimmers out of the water, as they did in the northern Mediterranean this past summer (Selby, flickr.com)

What do we do with that? Ignore it, I think, and continue to try to mitigate the extent of the changes. The new IPCC report clearly illustrates the different outcomes of different levels of atmospheric CO2, and the long-term advantages of stabilizing those levels soon are extraordinarily clear.

But Gershwin also writes about some of the remarkable biology of jellyfish, for they are more than just graceful but dangerous animals. Perhaps the most intriguing is one of a group of small species of the genus Turritopsis, which grow to about half a centimeter in diameter and are now common in most tropical and temperate oceans.

Turritopsis dohrnii medusa, about 1/2 cm in diameter, with a bright red stomach and a ring of tentacles (turritins.com)

Like most jelly fish, it has a two part life cycle. When jellyfish (medusae) are sexually mature, they shed eggs and sperm into the water, and then die. A fertilized egg develops into a tiny creeping planula larva that settles onto some hard substrate and then grows into a colonial hydroid or polyp that feeds on microplankton in the surrounding water. Eventually other buds on the hydroid develop into very small medusae which then escape and swim off.

Typical life cycle of a hydrozoan jellyfish (devbiol.com)

All Turritopsis do this, and because they are all small as adult jellyfish, less than 1cm in bell diameter, they are also very small when they first break free of their hydroid source, less than 1mm in diam.

When starved or physically damaged, where other jellyfish would just die, the medusae of this species instead can undergo an amazing transformation. The mouth and tentacles are resorbed, and the bell shrinks into a blob-like cyst that falls to the bottom, attaches to the substrate, and grows into a hydroid or polyp colony once again, reversing the usual life cycle. And there large numbers of new medusae develop, all clones of the original damaged medusa.

Reversing the usual life cycle, Turritopsis medusa ‘transdifferentiates’ back into a hydroid (newtimes.pl)

This is truly an extraordinary event, about as close to immortality as one can get.

Not surprisingly, as our medical use of stem cells grows ever greater, we are very interested in how cells that had been specialized for one function in the medusa ‘transdifferentiate’ into quite different cells in the hydroid.

Meanwhile, Turritopsis has spread around the world’s oceans, from Spain to Japan to South Africa, probably assisted by the ballast water of transport ships. It is wonderfully adapted to survive in this changing world, and may in turn play a role in the changes.

And it is also a reminder of how extraordinary it is to be a living being on Planet Earth, whether as a jellyfish or as a curious human.

Crossota alba is another small hydrozoan medusa, one that lives in deep water and drifts around in the dark, tentacles extended, preying on the plankton that it drifts into (whoi.edu)

Even in a more stable world, undisturbed by the collateral damage of a warming climate, sand beaches and dunes are forever growing, shrinking, changing shape and moving as storms and waves do their familiar work.

For decades the Army Corps of Engineers has defended the sandy coastline from Cape Cod to the southern tip of Florida, dredging or pumping up offshore sand to replenish eroding beaches, and plowing up sand ridges to prevent more wave and surge damage to coastal properties.

Their current efforts in both New Jersey and Florida are much in the news.

The ten miles of Miami Beach have depended on sand replenishment since the 1970s, but nearby sources of offshore sand have now run out. Where will more sand come from? North Carolina? The Bahamas? At what cost? And can there be a Miami Beach without a beach for tourists to frolic on?

Beach replenishment restored a beach front to Miami Beach, but now what? (geology.upm.edu

Meanwhile, for years the Army Corps of Engineers has been busy building sand ridges and dunes seaward of beach communities along the New Jersey coast. Where they have been prevented from building by beach-front homeowners, Hurricane Sandy did its most impressive damage. Most people who own such homes now recognize that having a dune blocking their view of the ocean is far better than having their home swept away, and have granted easements to have the remaining dunes built.

The New Jersey shore. Created ‘dunes’ protect parts of it, but they are only a short-term solution (nj.com)

The Army Corps of Engineers, here plowing up a ridge on the NJ shore, is charged with the impossible task of defending the coastline against the sea (usatoday.com)

Not all agree, of course, not wanting to lose their ocean views, and feelings have run high. Since dune protection isn’t much use if there are gaps in the dunes, the State’s Supreme Court has granted communities the ability to take ocean front space by eminent domain where holdouts refuse to grant easements, and the reamining dunes will no doubt soon be built.

Sand ridges plowed up in front of shore front homes will provide only short-term protection (fema.gov).

These are of course very short-term solutions. Beach replenishment is so clearly unsustainable, financially costly, and environmentally damaging, while plowing up sand ridges in front of beach-front homes does not make them dunes – they are temporary and unstable mounds of sand. These defenses will fail.

Instead, in the face of rising sea levels and increasingly intense storms, now is the time to initiate long-term responses. New Jersey’s Gov Christie understands this, and no doubt feels constrained by the stubbornness of coastal home owners. Florida’s Gov Rubio apparently does not accept the reality of climate change, so any leadership in Florida must continue to come from the county and municipal level.

Managed retreat is probably the best long-term option. The sand spits and barrier islands along the east coast should become free of human communities, left as sanctuaries and as natural buffers against the sea and climate changes that are occurring. We need their protection, and they need to be free to respond dynamically to the resculpting forces of winds and waves. Where barrier islands do not exist, communities need to retreat inland and to higher ground if it exists.

We can start this soon, with care and organized planning. If we wait, we will still have to do it, but it will be done in the face of catastrophe, the worst of circumstances.

And Miami Beach? Loss of its beaches is not its greatest problem. Miami is the US city most vulnerable to the impact of sea level rise, and it has nowhere to go.